1. Field of the Invention
The present invention relates to a zoom lens and an electronic imaging device having this zoom lens, and in particular, to a zoom lens which allows a slim design of a video camera, a digital camera, or any other electronic imaging device.
2. Description of Related Art
Recently, as the next generation camera of an alternative to a silver halide 35 mm film (135 format) camera, special attention has been devoted to a digital camera (an electronic camera). Such digital cameras have come to have many categories in a wide range from a high-function type for business use to a popular portable type.
The thickness of an optical system, notably a zoom lens system, from the most object-side surface to an imaging plane constitutes a chief obstacle to a reduction in depth of a camera.
The slim design technique of a camera body chiefly used in recent years adopts a so-called collapsible lens barrel that although the optical system protrudes from the front side of the camera body in photography, it is incorporated in the camera body when the camera is not used.
Examples of optical systems having possibilities that the collapsible lens barrel is used and the slim design can be effectively achieved are set forth in Japanese Patent Kokai Nos. Hei 11-194274, Hei 11-287953, and 2000-9997. Each of the optical systems includes, in order form the object side, a first lens unit with negative refracting power and a second lens unit with positive refracting power so that when the magnification of the optical system is changed, both the first lens unit and the second lens unit are moved.
The adoption of the collapsible lens barrel, however, requires much time to bring lenses into a working state from an incorporating state, which is unfavorable for use. Furthermore, the design that the most object-side lens unit is moved is unfavorable for water and dust proof. Also, there is physical restriction of fabrication limit size as to the direction of thickness of a lens part. The length of the collapsible lens barrel is governed by the thicknesses of lens parts, and thus even though further compactness of an image sensor is achieved in the future, the slim design of the camera in its depth according to the compactness cannot be expected.
On the other hand, in order to obtain a camera which does not have rising time (lens shifting time) required to bring the camera into the working state like the collapsible lens barrel, is favorable for water and dust proof, and is extremely small in depth, it is conceivable that the optical system is constructed so that the optical path (optical axis) is bent by a reflective optical component such as a mirror. In this case, even though the depth can be made small, the overall length of the optical path after being bent is increased, and hence dimensions other than that of the depth tend to become large. In this construction that the optical path is bent, however, it can be expected that when further compactness of the image sensor is realized in the future, the depth can be made small in accordance with the compactness. On the other hand, however, account must be taken of the influence of diffraction due to the compactness of the image sensor.